In ultrasonic welding (sometimes referred to as “acoustic welding” or “sonic welding”), two parts to be joined (typically thermoplastic parts) are placed proximate a tool called an ultrasonic “horn” for delivering vibratory energy. These parts (or “workpieces”) are constrained between the horn and an anvil. Oftentimes, the horn is positioned vertically above the workpiece and the anvil. The horn vibrates, typically at 20,000 Hz to 40,000 Hz, transferring energy, typically in the form of frictional heat, under pressure, to the parts. Due to the frictional heat and pressure, a portion of at least one of the parts softens or is melted, thus joining the parts.
During the welding process, an alternating current (AC) signal is supplied to a horn stack, which includes a converter, booster, and horn. The converter (also referred to as a “transducer”) receives the AC signal and responds thereto by compressing and expanding at a frequency equal to that of the AC signal. Therefore, acoustic waves travel through the converter to the booster. As the acoustic wavefront propagates through the booster, it is amplified, and is received by the horn. Finally, the wavefront propagates through the horn, and is imparted upon the workpieces, thereby welding them together, as previously described.
Another type of ultrasonic welding is “continuous ultrasonic welding”. This type of ultrasonic welding is typically used for joining fabrics and films, or other “web” workpieces, which can be fed through the welding apparatus in a generally continuous manner. In continuous welding, the ultrasonic horn is typically stationary and the part to be welded is moved beneath it. One type of continuous ultrasonic welding uses a rotationally fixed bar horn and a rotating anvil. The workpiece is pulled between the bar horn and the anvil. The horn typically extends longitudinally towards the workpiece and the vibrations travel axially along the horn into the workpiece. In another type of continuous ultrasonic welding, the horn is a rotary type, which is cylindrical and rotates about a longitudinal axis. The input vibration is in the axial direction of the horn and the output vibration is in the radial direction of the horn. The horn is placed close to an anvil, which typically is also able to rotate so that the workpiece to be welded passes between the cylindrical surfaces at a linear velocity, which substantially equals the tangential velocity of the cylindrical surfaces. This type of ultrasonic welding system is described in U.S. Pat. No. 5,976,316, incorporated by reference in its entirety herein.
In each of the above-described ultrasonic welding techniques, the workpieces to be joined are disposed between the horn and the anvil, during the welding process. The gap between the horn and anvil creates a pinching force that holds and compresses the workpieces while they are being joined. The physical characteristics of the product generated by an ultrasonic welding process are, in part, a function of the gap between the horn and the anvil. Thus, for the manufacture of a given product, a particular gap is desired. Therefore, it is desired that a mounting system for an ultrasonic welding system allow for the horn to be adjustably positioned along a vector, so that the horn is either closer to, or further from, the anvil, depending upon the desired gap.
Further, in the context of continuous ultrasonic welding, the longitudinal axis of the horn should be substantially parallel to the longitudinal axis of the anvil. Such an arrangement generally ensures that the gap exhibited between the anvil and the horn is substantially constant along the length of the horn. Accordingly, it is further desired that a mounting system permit the longitudinal axis of the horn to be adjusted, so as to be substantially parallel with the longitudinal axis of the anvil.
Still further, because the physical characteristics of the product generated by an ultrasonic welding process are, in part, a function of the relative positions of the horn and the anvil, it is desirable that the mounting system substantially eliminates degrees of freedom of the horn and anvil not needed to either adjust the gap between the horn and the anvil or to bring the longitudinal axis of the horn into a parallel relation to the longitudinal axis of the anvil.